The importance of semiconductor emitters and detectors is rapidly increasing along with progress in the opto-electronic field, such as optical fiber communication, optical data processing, storage and solid state laser pumping.
Quantum dots formed by the Stranski-Krastanow growth mode which is obtained as deposit of the highly strained material on a substrate is promising for developing zero dimensional quantum devices for light emitting sources and detectors.
Quantum dot infrared photodetectors are one of the promising applications for semiconductor devices based on zero dimensional quantum structures. There is an increasing need for sources and detectors for mid and far infrared spectral regions due to the broad range of the applications such as IR spectroscopy of chemical analysis, remote sensing, and atmospheric communications. Similar to the case of quantum well intersubband photodetectors (QWIPs), quantum dots are expected to play an important role in infrared photodetectors. Compared to QWIPs, quantum dot detectors have advantages such as a slowing of the intersubband relaxation time due to reduced electron-phonon interaction. In addition, unlike a quantum well, quantum dots are sensitive to normally incident photons due to the breaking of the polarization selection rules.
Recently, long wavelength infrared (LWIR) intersubband absorption in the range of 60 meV.about.120 meV from InAs/(Al)GaAs, normal incidence LWIR intersubband absorption around 88 meV from InGaAs/GaAs, and LWIR intersubband absorption around 150 meV from n-doped InAs/GaAs quantum dots have been reported. Also mid-infrared photoconductivity in InAs/AlGaAs at near 3 .PHI.m has been observed.